Analysis of Load Balancing Limits for Cascaded Rectifiers

Cascaded H-bridge rectifiers have recently been increasing applied due to its lots of advantages. However, the load imbalance of the cascaded H-bridge rectifier will induce the DC-link capacitor voltages to be unbalanced, which will cause the semiconductor device to withstand overvoltage and even cause the dc-link capacitor to breakdown and instability of the converter system. Quantitative assessment the load balancing limits is significant for operating stably and system parameter design. This paper presents the working principle, control and modulation methods of cascaded H-bridge rectifier. Based on power balance and modulation principle, a calculation method of the load balancing limits for two-cell cascaded H-bridge rectifiers is proposed. Simulation results are given to validate the correctness of the proposed calculation method. The results show if the load imbalance exceeds the balance control range, additional current harmonics will be generated in AC side.